Polypeptide synthesis in brain. We expect to concentrate on the biosynthesis of the hypothalamus-produced tripeptide, pyro-Glu-His-Pro- NH2, the thyrotropin release hormone. Preliminary experiments have been disturbed by the presence of high, partly specific, peptidase activity. It may become more amenable by use of inhibitors of specific tissue peptidases which prevent product destruction, such as pyro-Glu- His-O.Me. Attempts towards the hypothalamic biosynthesis of the luteinizing release hormone LRH are in progress. Tyrocidine synthesis. The function and isolation of the phosphopantetheine-containing peptidyl carrier protein will be continued. We foresee the possibility of returning to the more stable enzymes of the gramicidin S synthesis for obtaining large quantities of a pure polyenzyme. Attempts will be made to isolate cell-free systems for the biosynthesis of valinomycin and rhodotorulic acid in the hope of identifying more thioesterlinked peptide synthesizing systems. Biosynthesis and function of guanosine 5',3'-polyphosphates. The recently discovered methanol-stimulated, nonribosomal synthesis of ppGpp and pppGpp (magic spot compounds I and II) by the salt wash of stringent E. coli ribosomes is to be compared with the ribosome-dependent synthesis, and the enzyme is to be purified. Attempts to explore the possible function of these guanosine polyphosphates in protein synthesis are being considered. Their formation in relaxed organisms and the inhibition by ongoing polypeptide synthesis will be studied.